ARTICLE FEED & ADDITIVE MAGAZINE November 2024 71 answer, it is essential to understand the mechanisms behind the formation of these dark spots and the underlying causes of their development. THE LINK TO INFLAMMATION Melanin pigments in the flesh of salmon are linked to inflammation in the fillet. While the exact cause of the problem is unclear, the process typically begins with a bleed or trauma in the flesh, triggering melanin-producing cells – melanomacrophages, as a part of the immune response to fight or seal off the pathogens and clean up the damage caused by the trauma. Recent science has also linked the initiation to hypoxia and necrosis of fat cells that triggers the inflammation cascade in the fillet. If the inflammatory response is optimal, the immune system cleans up the damage, and the fillet returns to a healthy state. However, if the inflammatory process becomes chronic and the fish does not return to a healthy state, the pigments continue to accumulate in the fillet, thus compromising the fillet quality. Chronic inflammation in animals, including salmon, has been linked to long term exposure to stress. Stressors in intensive farming environments include diseases, rough weather, and handling procedures. One way to combat chronic inflammation is by ensuring sufficient omega-3 intake, specifically EPA and DHA fatty acids. These fatty acids are part of the anti-inflammatory pathways in the immune system and may reduce the chance of an inflammatory process becoming chronic and harmful. Research has shown that low levels of EPA and DHA in fish feed is associated with less robust fish that are prone to chronic stress. Access to antioxidants will also influence the oxidative state in the musculature, and may also impact the development of dark spots in the fillet. Several researchers have investigated the impact of increased EPA and DHA levels on melanin occurrence in the fillet. In a comprehensive report (EX-spot 2022), the authors concluded that higher EPA and DHA levels clearly reduced the severity of the melanosis. They also found that DHA, in particular, seems to inhibit tyrosinase, an enzyme that is involved in the production of melanin pigments in the cells. 25 Dark spots, % 3 - 5 5 -7,5 7,5 - 10 35 30 25 20 15 10 5 0 14 EPA+DHA, % of Fatty acids in feed 11 Rapport+27-2022+EX-spot: Dark spots in salmon fillet. Cause of dark spots and preventive measures Figure 1
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